Laser machining apparatuses have been extensively used in conjunction with numerical control systems, since such an arrangement facilities complex shape machining of a workpiece at high speed. Generally, no problems exist in machining a workpiece along a straight line or a curve of a large radius of curvature. However, if the output of the laser beam is not controlled in accordance with the moving speed of the workpiece during machining of corner portions or acutely angled edge portions thereof, welding losses occur due to build up of thermal energy and excessive heat absorption, resulting in decreased machining accuracy and causing to degradation of the material of the workpiece.
In order to avoid such drawbacks, a laser output controlling method has been proposed in Japanese patent application No. 62-107824 whereby the laser output is controlled in accordance with machining speed during machining of edge portions.
Conventionally, as in the above-mentioned application, the laser output is controlled in response to an instructions regarding the moving speed of the workpiece as calculated by a machining program.
However, with such a laser output controlling method, there is a significant time delay between the occurrence of the instruction and the movement of the mechanical system controlled by the instruction due to the inertia of the mechanical system. On the other hand, substantially no time delay is involved in outputting the laser beam, since the laser output is controlled by a current flowing in a discharge tube.
Specifically, the response time of the laser output is smaller by approximately a factor of two than that of the mechanical system. The control of the laser output in response to the moving instructions for the mechanical system causes a loss of synchronism between the moving speed of a work table and the laser output. For this reason, there have been cases where machining accuracy and machining performance were not sufficiently attained.